Spinal fixation systems typically require the threaded securement of some form of bone anchor and the like or bone screw-assembly into two or more vertebrae, as well as which requires the drawing of the rod to the anchors/screw-assemblies, or drawing the anchors/screw-assemblies to the rod. An exemplary bone screw-assembly 10, shown in FIG. 6, may be used with at least one other such assembly to secure a stabilization rod 19 and includes a pedicle screw 12 and a body member 14. The pedicle screw 12 may include a substantially spherical or elliptical head portion 24 defining a slot therein used to drive a threaded tube portion 28 into a vertebra. The body member 14 is generally cylindrical in configuration and adapted to receive the head portion 24 that cooperates therewith so as to define a modified ball-joint. This design allows for variable angular movement of the body member 14 with respect to the pedicle screw 12 with the threaded tube portion 28 extending through an opening 26 in the end of the body member 14. The body member 14 additionally defines a pair of opposed parallel slots (or a single slot) axially disposed in the side wall thereof forming a saddle to receive a portion of the fixation rod 19. A set screw 18, shown in FIG. 7, is used to threadably engage the body member 14 of the screw assembly 10 to secure the stabilizing rod 19 within the body member 14.
In various exemplary surgical procedures, one or more tubes may be coupled to the body member 14 prior to insertion of the set screw. The tubes may extend posteriorly away from the vertebra and may facilitate derotation and alignment of the spine, insertion of the rod, and insertion of set screws to rigidly fix the rod to the body member. For example, the tubes may include any of screw extender tubes, inner reduction tubes, outer sleeves of instruments, and outer reduction tubes in one or more configurations. A separate tool may be necessary to either draw the fixation rod down into the opposed slots in the body member of the screw assembly or, when necessary, to draw the pedicle screw and attached vertebrae outwardly to the rod to effect the desired alignment of the vertebrae and the securement of the rod. A screw driver may be used to insert the set screw through one or more of the tubes and to tighten the set screw after insertion of the rod.
Typically, the set screw is placed on the tip of the screw driver prior to insertion through one of the tubes at the surgical site. Typically, a friction fit may be employed between the set screw and the tip of the screw driver. Therefore, the set screws may fall off the screw driver onto the floor, into one of the tubes, or into the surgical site thus complicating the surgery with delays and possible contamination. The invention described herein may be used with any system that utilizes one or more tubes as described above to reduce the risk of any of these and other complications.